1. Field of the Invention
The present invention relates to an electrostatic charge regulator useful, for example, as an electrophotographic material or an electrostatic printing material, as well as a method for making the same and an image forming method using the same.
2. Description of the Related Art
Heretofore, as techniques which positively utilize an electric charge induced by static electricity there have been known such electrostatic recording techniques as electrophotography and electrostatic printing. In the electrostatic recording method, at the time of developing a formed electrostatic charge latent image, there is used a charging member for imparting an appropriate amount of a positive or negative electric charge to colored fine particles called toner.
Particularly, in the electrophotographic method as an electrostatic recording method, which utilizes an electrostatic charge induced by frictional charging, there can be made a broad classification into a dual-component developing method and a mono-component developing method according to charging mechanisms used. The dual-component developing method uses what is called a carrier coated with a resin and capable of imparting a frictional charge to various electrically conductive, fine particulate toners. On the other hand, the mono-component developing method uses what is called a sleeve or a blade formed by coating an electrically conductive, cylindrical base or thin plate with a resin or the like in the same manner as above.
However, a problem has been encountered in utilizing such a frictional charge. More particularly, in case of creating an electric charge by frictional charging with use of the foregoing charging member, there occurs a phenomenon such that the electric charge created is too low or too high, depending on the type of the coating resin used as the charging member or depending on the charging environment. Due to such a phenomenon, an electrostatic charge latent image formed cannot be reproduced accurately and an image which is rendered visible becomes worse. Moreover, in the method wherein an electric charge is generated by frictional charging, there is a fear that the coated resin layer may be peeled off by friction or the surface thereof may be stained, thus giving rise to the same phenomenon as above.
In the above electrostatic recording methods, also as to a transfer member to be used in the process of transferring the toner onto paper and making an image visible, thin polymer films with controlled resistance have recently been used to match the recent simplification of the apparatus concerned.
Such thin polymer films contain a resistance regulating material such as carbon black in a dispersed state for controlling resistance, which material, however, is a low resistance material for obtaining a desired resistance value, so that there occurs an intra-surface unevenness in resistance, depending on the state of dispersion of the material, with consequent deterioration of reliability.
In an effort to solve the above-mentioned problems, various resins and additives for use in the charging member have so far been studied in connection with the dual-component developing method in electrophotography. For example, there are proposed carriers coated with resins containing fluorine polymers as in Japanese Published Unexamined Patent Application Nos. Sho 49-51950, Sho 57-99653, and Sho 60-202451, containing silicone polymers as in Japanese Published Unexamined Patent Application Nos. Sho 60-19156, Sho 62-121463, Sho 61-110159, and Sho 61-110160, or containing silicone oils as in Japanese Published Unexamined Patent Application Nos. Hei 3-46669, Hei 3-46670, Hei 3-46671, and Hei 5-72814.
However, the abrasion resistance of the resin coatings is insufficient, an initial charging value varies largely at high temperature and high humidity or at low temperature and low humidity, there occurs an expansion in charge distribution of the toner used, particularly, the amount of an electric charge decreases at high temperature and high humidity or increases to an extreme extent at low temperature and low humidity. Thus, as to environmental stability, there still remains room for improvement.
Also with respect to the electrostatic recording method, studies are being made about the mono-component developing method not using a carrier as the charging member in view of the recent tendency to the reduction in size, which method utilizes friction with a blade or a sleeve for charging a toner used. However, the blade or sleeve is kept in friction with the toner, so also for such blade or sleeve it is important to hold an appropriate amount of an electric charge over a long period as is the case with the foregoing dual-component developing method. For example, in Japanese Published Unexamined Patent Application No. Hei 3-204664 there is used a curable fluorine-containing copolymer as the material of a developing roller. But this roller is deficient in its power of charging a toner, thus giving rise to the problem that an image having been rendered visible is deteriorated.
As to the foregoing transfer member, there has been made an attempt of using a homogeneous, electrically conductive, high molecular compound for solving the above-mentioned problems, as is described, for example, in Japanese Published Unexamined Patent Application No. Hei 9-90776. But also in this case a problem is encountered in point of environmental stability of the electrically conductive polymer. Particularly, the collapse of a transferred image has been unavoidable at high temperature and high humidity and at a reduced resistance.
The present invention has been accomplished in view of the above-mentioned problems involved in the related art and provides an electrostatic charge regulator capable of holding a desired electric charge stably in any of the above techniques which utilize an electrostatic charge, as well as a method for making the electrostatic charge regulator and an image forming method which uses the electrostatic charge regulator and which can form a stable image in good environmental stability while holding an electric charge stably.
According to the present invention, the foregoing problems can be solved by the following configuration.
The electrostatic charge regulator according to the present invention is characterized by having a base member and a surface layer, the surface layer containing a non-linear resistor.
The method for making the electrostatic charge regulator according to the present invention is characterized in that the surface layer is formed by forming a thin film of a composite metal oxide on the base member or by using dispersion of powder of the composite metal oxide in a high molecular compound, the composite metal oxide being prepared by using at least one member selected from Group A metals (Zn, Ti, Si, Al, Zr) and at least one metal selected from Group B metals (Bi, Sb, C, Y, La, Pr, Sc, Ce, Sn, Pb).
The image forming method according to the present invention is characterized by using the electrostatic charge regulator.
The electrostatic charge regulator according to the present invention is characterized by being used for toner.
In the electrostatic charge regulator according to the present invention, a non-linear resistor is contained in the surface layer and a threshold voltage of the non-linear resistor exerts a great influence on the characteristics of the regulator and also influences an insulator surface on which an electrostatic charge is generated, whereby the amount of an electric charge on the insulator surface can be adjusted.
In the method for making the electrostatic charge regulator according to the present invention, the surface layer is formed on the base member by using a combination of a Group A metal with a Group B metal and, if necessary, other metals, and there is obtained a non-linear resistor having a desired threshold voltage by the method of making.
In the image forming method according to the present invention, if there is used the electrostatic charge regulator having the surface layer containing the non-linear resistor and formed on a carrier, a developer sleeve, a developer blade, or a transfer belt, as the base member, then the amount of an electric charge in each layer is held stably and there occurs no image deterioration.